Conventionally, a sheet article such as a document or a photo is usually covered with a protective film for protection because such a sheet article is readily suffered from damage. Typically, a sheet laminating apparatus (or a laminator) is used for heating and pressing (or laminating) a sheet article between two pieces of protective films in order to achieve the protective purpose. Hereinafter, the configurations of a conventional sheet laminating apparatus will be illustrated with reference to FIG. 1.
FIG. 1 is a schematic cross-sectional view illustrating a conventional sheet laminating apparatus. As shown in FIG. 1, the sheet laminating apparatus 1 comprises a heat-treating mechanism 10, a transmitting and pressing mechanism 11 and a transfer passage 12. The heat-treating mechanism 10 includes a heater 101 and an electrically-heated plate 102. The external surface of the transmitting and pressing mechanism 11 is enclosed by the heater 101. In addition, the heater 101 is separated from the transmitting and pressing mechanism 11 by a gap.
The process for laminating a sheet article (not shown) by using the sheet laminating apparatus 1 will be described as follows. First of all, the sheet article is sandwiched between an upper thermoplastic film and a lower thermoplastic film to form a sandwich structure. Then, the sandwich structure is fed into the transfer passage 12 through an entrance 121. By means of the transmitting and pressing mechanism 11, the sandwich structure is continuously transported through the passage 12. During this stage, the electrically-heated plate 102 of the heat-treating mechanism 10 transforms electricity to heat energy so as to preheat the sandwich structure. The heat energy generated by the electrically-heated plate 102 is uniformly distributed over the heater 101, and radiated through an air gap between the heater 101 and the transmitting and pressing mechanism 11 so as to heat up the transmitting and pressing mechanism 10. The transmitting and pressing mechanism 11 presses against opposite sides of the sandwich structure that is transported through the transfer passage 12, and transmits the heat energy to the sandwich structure so as to soften the thermoplastic films. After being transmitted and pressed by the transmitting and pressing mechanism 11, the sheet article bonds with the softened thermoplastic films to form a laminate structure. Meanwhile, the sheet article is fixed between these two pieces of thermoplastic films.
For enhancing the laminating efficacy, the sheet laminating apparatus 1 should to be adjusted at a proper hot press temperature according to the thickness of the sheet article to be laminated. Since the heater 101 is relatively thick, it is time-consuming to uniformly distribute the heat over the heater 101. Under this circumstance, the transmitting and pressing mechanism 11 is slowly heated up. Since it takes a waiting time to heat up the transmitting and pressing mechanism 11, the conventional sheet laminating apparatus 1 is not user-friendly. For solving the above drawbacks, Taiwanese Patent No. 484589 has disclosed a method for increasing the speed of heating up the transmitting and pressing mechanism by reducing the thickness of the heater 101.
FIG. 2 is a schematic cross-sectional view illustrating another conventional sheet laminating apparatus disclosed in Taiwanese Patent No. 484589. As shown in FIG. 2, the sheet laminating apparatus 2 comprises two rollers 21 (i.e. the transmitting and pressing mechanism), a heat-conducting case 22 (i.e. the heater) and a heat generator 23. The rollers 21 are enclosed by the heat-conducting case 22. The heat generator 23 is mounted in the heat-conducting case 22 for transferring heat to the heat-conducting case 22. Since the heat-conducting case 22 is thin and flat, the rollers 21 enclosed by the heat-conducting case 22 are quickly heated up to the working temperature.
The sheet laminating apparatus, however, still has some drawbacks. For example, due to the thin heat-conducting case 22, the heat is dissipated away fast and the heat loss is considerable. Under this circumstance, the working temperatures of the rollers 21 become unstable and thus the laminating efficacy is unsatisfied. Moreover, since large portions of the rollers 21 are enclosed by the heat-conducting case 22, the overall volume of the heat-conducting case 22 is still huge. In other words, the sheet laminating apparatus 2 is not cost-effective.